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Instrumentation Symbols and Identification

Approved 18 September 2009

ANSI/ISA-5.1-2009, Instrumentation Symbols and Identification ISBN: 978-1-936007-29-5

Copyright © 2009 by ISA. All rights reserved. Not for resale. Printed in the United States of America. No part of this publication may be reproduced, stored in a retrieval system, or transmitted in any form or by any means (electronic, mechanical, photocopying, recording, or otherwise), without the prior written permission of the Publisher.

ISA 67 Alexander Drive P. O. Box 12277 Research Triangle Park, North Carolina, 27709 USA

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Preface (informative)

This preface is included for information purposes and is not part of ANSI/ISA-5.1-2009.

This standard has been prepared as part of the service of ISA, The International Society of Automation, toward the goal of uniformity in the field of industrial automation. To be of continuing value, this standard should not be static but should be subject to periodic review. ISA welcomes all comments and suggestions and asks that they be addressed to the Secretary, Standards and Practices Board; ISA; 67 Alexander Drive; P. O. Box 12277; Research Triangle Park, NC 27709; Telephone: (919) 549-8411; Fax: (919) 549-8288, e-mail: standards@isa.org

The ISA Standards and Practices Department is aware of the growing need for attention to the metric system of units in general, and the International System of Units (SI) in particular, in the preparation of instrumentation standards. The Department will endeavor to introduce SI-acceptable metric units in all new and revised standards, recommended practices, and technical reports to the greatest extent possible. Standard for Use of the International System of Units (SI): The Modern Metric System, published by the American Society for Testing & Materials as IEEE/ASTM SI 10-97, and future revisions, will be the reference guide for definitions, symbols, abbreviations, and conversion factors.

It is the policy of ISA to encourage and welcome the participation of all concerned individuals and interests in the development of ISA standards, recommended practices, and technical reports. Participation in the ISA standards-making process by an individual in no way constitutes endorsement by the employer of that individual, of ISA, or of any of the standards, recommended practices, and technical reports that ISA develops.

ANSI/ISA-5.1-2009 - 4 -

Users may find the following book of value in applying ANSI/ISA-5.1-2009:

Control System Documentation: Applying Symbols and Identification, Thomas McAvinew w.isa.org/books.

Users of this standard are asked to send comments or suggestions to standards@isa.org

The following served as voting members of the ISA5 Committee during development of ANSI/ISA-5.1- 2009.

Name Affiliation

Alvin Iverson, Chair Ivy Optiks Ian Verhappen, Managing Director Industrial Automation Networks Inc Thomas McAvinew, Past Managing Director Jacobs Engineering James Carew, Chair, ISA5.1 Consultant Gerald Barta Mustang Engineering LP Donald Frey Reliatech Inc Alex Habib Consultant Ganesier Ramachandran Shell Global Solutions US

On behalf of the ISA5 Committee and the ISA Standards & Practices Board, we wish to recognize and thank James Carew for his outstanding work, technical expertise, and commitment in leading the revision of this widely used ISA standard, and Thomas McAvinew for his valuable technical and editorial contributions.

Al Iverson, ISA5 Chair Ian Verhappen, ISA5 Managing Director

The ISA Standards and Practices Board approved this standard on 23 July 2009 Name Affiliation

J. Tatera Tatera & Associates Inc. P. Brett Honeywell Inc. M. Coppler Ametek Inc. E. Cosman The Dow Chemical Company B. Dumortier Schneider Electric D. Dunn Aramco Services Co. R. Dunn DuPont Engineering J. Gilsinn NIST/MEL E. Icayan ACES Inc. J. Jamison Husky Energy Inc. D. Kaufman Honeywell K. P. Lindner Endress + Hauser Process Solutions AG V. Maggioli Feltronics Corp. T. McAvinew Jacobs Engineering G. McFarland Emerson Process Mgmt. Power & Water Sol. R. Reimer Rockwell Automation N. Sands DuPont

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H. Sasajima Yamatake Corp. T. Schnaare Rosemount Inc. I. Verhappen MTL Instrument Group R. Webb ICS Secure LLC W. Weidman Worley Parsons J. Weiss Applied Control Solutions LLC M. Widmeyer Consultant M. Zielinski Emerson Process Management

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1 Purpose13
2 Scope13
3 Definitions17
4 Identification letters table25
5 Graphic symbol tables31
6 Graphic symbol dimension tables76
Annex A Identification system guidelines (informative annex)85
Annex B Graphic symbol guidelines (informative annex)1
Table 4.1 — Identification letters30
Table 5.1.1 — Instrumentation device and function symbols36
Table 5.1.2 — Instrumentation device or function symbols, miscellaneous37
Table 5.2.1 — Measurement symbols: primary elements and transmitters38
Table 5.2.2 — Measurement symbols: measurement notations (4)39
Table 5.2.3 — Measurement symbols: primary elements40
Table 5.2.4 — Measurement symbols: secondary instruments43
Table 5.2.5 — Measurement symbols: auxiliary and accessory devices4
Table 5.3.1 — Line symbols: instrument to process and equipment connections45
Table 5.3.2 — Line symbols: instrument-to-instrument connections46
Table 5.4.1 — Final control element symbols48
Table 5.4.2 — Final control element actuator symbols50
Table 5.4.3 — Self-actuated final control element symbol52
Table 5.4.4 — Control valve failure and de-energized position indications5
Table 5.5 — Functional diagramming symbols56
Table 5.6 — Signal processing function block symbols57
Table 5.7 — Binary logic symbols64
Table 5.8 — Electrical schematic symbols72
Table 6.1 — Dimensions for Tables 5.1.1 and 5.1.278
Table 6.2 — Dimensions for Tables 5.2.1, 5.2.2, 5.2.3, 5.2.4, and 5.2.579
Table 6.3 — Dimensions for Tables 5.3.1 and 5.3.280
Table 6.4 — Dimensions for Tables 5.4.1, 5.4.2, 5.4.3, and 5.4.481
Table 6.5 — Dimensions for Table 5.582
Table 6.6 — Dimensions for Table 5.682
Table 6.7 — Dimensions for Table 5.783
Table 6.8 — Dimensions for Table 5.884

Contents Table A.1 — Typical Loop and Instrument Identification/Tag Numbers.....................................................9

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Table A.2.1 — Allowable letter/number combinations for loop numbering schemes and first letters A to O


Table A.2.2 — Allowable letter/number combinations for loop numbering schemes and first letters P to


Table A.2.3 — Allowable letter/number combinations for loop numbering schemes and first letters W to


Table A.3.1.1 — Allowable succeeding letters for readout/passive functions aand ffirst letters A to O (1)


Table A.3.1.2 — Allowable succeeding letters for readout/passive functions and first letters P to VZZ (1)


Table A.3.1.3 — Allowable succeeding letters for readout/passive functions and first letters W to ZDZ (1)


Table A.3.2.1 — Allowable succeeding letters for output/active function letters and first letters A to O (1)

(1) (4b2)107

Table A.3.2.2 — Allowable succeeding letters for output/active function letters and first letters P to VZZ

(1) (4b2)108

Table A.3.2.3 — Allowable succeeding letters for output/active function letters and first letters W to ZDZ Table A.4 — Loop and Identification Tag Number suffixes (1) (2)............................................................109

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Introduction (informative)

(1) This introduction, as well as any footnotes, endnotes, and informative annexes, is included for information purposes and as background on the evolution of this standard and not as a normative part of ANSI/ISA-5.1-2009.

(2) The instrumentation symbolism and identification systems described in this standard accommodate advances in technology and reflect the collective industrial experience gained since the original ISA Recommended Practice RP-5.1, published in 1949, was revised, affirmed, and subsequently published as ANSI/ISA-5.1-1984, and then reaffirmed in 1992.

(3) This 2009 version attempts to strengthen this standard in its role as a communication tool in all industries that depend on measurement and control systems to operate and safeguard their manufacturing processes, machines, and other equipment. Communication presupposes and is facilitated by a common language. This 2009 version of the standard continues to build on the foundation for that common language.

(4) When integrated into a system, the designations and symbols presented here form a dedicated language that communicates concepts, facts, intent, instructions, and knowledge about measurement and control systems in all industries.

(5) The 1949 recommended practice and the 1984 standard were published as non-mandatory rather than as mandatory consensus documents. As such, they had many of the strengths and the weaknesses of such standards. Their primary strength was that they could be used in widespread, interdisciplinary ways. Their main weakness was that they were not specific enough, in some cases, to satisfy the special requirements of particular interest groups.

(6) This revision is published as a consensus standard and contains both mandatory and non-mandatory statements that have been reviewed and approved by a large group of practitioners in the field of instrumentation and control. This group was well versed in the use of identification and symbol systems as a means of communicating the intent of measurement and control systems to all that need such information. It is hoped that the consensus reached by this group regarding what is mandatory and what is not will enhance the strengths and lessen the weaknesses of the previous issues.

(7) Versions of this standard have been in use for more than fifty years, and most of the identification letter and symbol meanings or definitions that were contained in ISA-RP5.1-1949 and ISA-5.1-1984 (R 1992), have taken on a proprietary nature and have become accepted industry practice and assumed to be mandatory. The meanings and definitions of new symbols will be mandatory. This action is being taken in response to questions and comments that occur frequently because of unclear definitions.

(8) Mandatory definitions or meanings for letters used in identification and for symbols used in graphic depiction of measurement and control devices and functions are given. Mandatory minimum symbol dimensions are given. Informative identification and graphic symbol guidelines include alternate identification and symbol definitions and usage methods. Consistency is the one criterion that should govern the selection and application of identification and graphic schemes.

(9) This standard has been viewed in the past as being oriented to the oil and chemical process industries. This perception, while not intended, resulted from the fact that people who wrote the original and previous revisions were mainly working in those industries. It is the intent of the ISA5 committee that ISA Technical Reports will be used to address this type of problem. It is hoped that the technical report format will be specific enough to satisfy the special requirements of particular interest groups by providing examples and guidelines for use of the identification and symbolization methods for specific industries. These industries include, but are not limited to, metal refining, power generation, pulp and paper, and discrete parts manufacturing. The technical report format presents the best approach for making this standard applicable to industries that may have many usages and accepted practices that are not used in

ANSI/ISA-5.1-2009 - 10 - the process industries.

(10) The extensive examples in previous versions of this standard that illustrated identification and symbolization definitions and methods have been removed and will be moved to technical reports that will be prepared after publication of this revised standard.

(1) The symbols and identification methods contained in this standard have evolved by the consensus method and are intended for wide application throughout all industries. The symbols and designations are used as conceptualizing aids, as design tools, as teaching devices, and as a concise and specific means of communication in all types and kinds of technical, engineering, procurement, construction, and maintenance documents, and not just piping and instrumentation diagrams (P&IDs).

(12) Previous versions of this standard have been flexible enough to serve all of the uses just described, and it must continue to do so into the future. To this end, this revision clarifies the definitions of symbols, identification, and definitions for concepts that were previously described, such as, for example, shared display/control, distributed control, and programmable control. It also adds definitions for new symbols required for functional diagramming of instruments and simple electrical circuit diagrams.

(13) This revision extensively changes the format of ANSI/ISA-5.1-1984 (R 1992). Clauses 1, 2, and 3 are essentially the same as previously written with some additions and modifications. Clauses 4, 5 and 6 and informative Annexes A and B are new or extensively revised.

(14) Clause 4, “Identification letter tables,” was previously Clause 5, “Tables.” It is almost the same as the previous version and deals only with Table 4.1, “Identification letters,” which was previously Table 1, “Identification letters.”

(15) Clause 5, “Graphic symbol tables,” is a new clause that contains new symbols and the symbols that were previously in Clause 6, “Drawings,” presented in a table format that includes text describing the application of the symbols but no examples of their use.

(16) Clause 6, “Graphic symbol dimension tables,” is a new clause that establishes minimum mandatory dimensions for the symbols shown in the tables in Clause 5 when used in the preparation of full-size engineering drawings.

(17) Annex A, “Identification system guidelines (Informative),” was previously Clause 4, “Outline of the Identification System,” and presents the most commonly used instrumentation and function identification methods. Included are expanded “Allowable loop and function letter combination” tables and added “Allowable loop letter scheme” tables.

(18) Annex B, “Graphic symbol guidelines” (Informative), is a new informative clause that replaces the examples formerly given in Clause 6, “Drawings,” to provide some limited assistance in the application of the symbols in Clause 5.

(19) Definitions for identification letters and symbols are now mandatory to reduce the confusion caused by giving meanings to identification and symbols not intended by this standard. At the same time, the number of symbology and tagging bubbles required to depict a measurement or control scheme was allowed to range from “everything must be shown” to the “minimum required to convey the instrumentation and functionality required.” Guidelines are intended to aid in the application of identification and symbology and to include some of the known methods as alternate usages.

(20) The meanings of ‘shared display, shared control,’ and ‘programmable logic control’ have been clarified and expanded because of changes in technology and usage since their inception in ISA-5.3- 1983, “Graphic Symbols for Distributed Control/Shared Display Instrumentation, Logic and Computer Systems.” The commonly assumed meanings of ‘circle-in-square’ as distributed control system (DCS) functions and of ‘diamond-in-square’ as programmable logic controller (PLC) functions are no longer

- 1 - ANSI/ISA-5.1-2009 accurate because they no longer reflect the currently acceptable meanings. DCSs and PLCs can both perform continuous and binary control functions. The same functions are performed by personal computers (PC) and by fieldbus and devicebus devices. Both ‘circle-in-square’ and ‘diamond-in-square’ symbols are classified as ‘shared display, shared control.’ ‘Circle-in-square’ will depict either (a) primary control system choice or (b) basic process control system (BPCS). ‘Diamond-in-square’ will depict either (a) alternate control system choice or (b) safety instrumented system (SIS). Users who continue to use the symbols as in the past should change to the revised meanings as soon as possible.

(21) This revision uses, with permission, information from the excellent SAMA (Scientific Apparatus Makers Association) PMC 2.1-1981, “Functional Diagramming of Instrument and Control Systems,” a document still used by many control system engineers and designers. SAMA symbols and descriptions for functional diagramming of Instruments and control loops and for signal processing symbols and function blocks were adapted in ANSI/ISA-5.1-1984 (R 1992) for use in loop schematic diagrams. This revision adds the SAMA symbols and descriptions for logic function enclosures for use in functional diagrams, logic diagrams, and application software functions. Guidelines for a limited number of applications of the symbols will be found in Annex B, “Graphic symbol system guidelines (Informative).”

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